Spray painting of irregularly shaped articles by automatic production means often presents a problem in achieving an adequately uniform coating of the workpiece surfaces. Whether utilizing electrostatic or non-electrostatic spray coating techniques, the automatic spray coating of a part having a variety of surface exposures conventionally may require a complex initial setup of the spray heads, to direct spray from various angles and in various directions, in order to be assured of applying coating material to all of the surface exposures.
A unique and improved new method and apparatus for achieving a highly satisfactory spray coating of irregular workpieces is disclosed in the co-pending Application of Richard F. Wiggins, Ser. No. 637,019, filed Dec. 2, 1975 now U.S. Pat. No. 4,042,734, and owned by the Gyromat Corporation. The invention of the earlier application enables efficient coating of workpieces of extremely large sizes, having surface areas exposed along various axes. Pursuant to the teachings of the earlier application, one or more spray heads are mounted for rotary movement about a predetermined axis. The spray head or heads are in turn disposed at a substantial angle to the rotational axis (typically around 45.degree.) such that, when the spray heads are rotated about a horizontal axis (for example) the spray fans emanating from the spray heads will, at one time or another, traverse most surfaces which are either in front of, above or below, or to either side of the rotating spray heads. In an automatic spray coating line, the workpiece to be coated is conveyed through a spray housing past a coating station at which the rotating spray heads are located. The spray heads are reciprocated more or less at right angles to the path or axis along which the workpiece is conveyed, so that the rotating nozzles sweep the work from end to end and also from top to bottom.
In a paint spray system such as described above, the proper positioning of the spray heads adjacent the workpiece is important to insure an even and uniform application of the spray. Typically, workpieces of varying width are mounted on the conveyor in no particular order. To accommodate the various pieces, the spray heads are mounted on a positioner so that they may be moved along a line perpendicular to the plane defined by the workpiece and positioned at a point optimum for spraying the particular piece.
The present invention relates to a unique, automatic part gaging and spray head positioning system operative to sense the configuration of an incoming part and position the spray heads accordingly. The new system is most advantageously used in conjunction with the aforementioned Wiggins application. However, the invention is not exclusively limited to such utilization, as will appear.
In accordance with one aspect of the invention, a part sensing element is positioned adjacent the conveyor, shortly in advance of the entrance door of the spray coating chamber, and is connected to a position memory apparatus. As a workpieceapproaches the coating chamber, the sensing element is laterally displaced to make contact with the incoming workpiece, and the position memory apparatus functions to translate such lateral displacement into part width information, which is stored in a storage memory. The stored information is then utilized to control the spray head positioner to place the spray heads at an optimum distance from the particular workpiece during the coating operation.
In the illustrated form of the invention, the sensing element is connected to a limit switch apparatus and a doubleacting actuator. A workpiece approaching the coating chamber activates the forward drive of the actuator to displace the sensing element towards the workpiece. The displacement of the sensing element will operate the limit switch apparatus in accordance with the distance the sensing element is displaced. The limit switch apparatus is electrically connected to a storage memory which retains the part shape information thus derived for utilization at the appropriate times.
A novel electrical control means is provided to operate the spray head positioner to properly position the spray heads in accordance with the information stored in the above described part gaging cycle. In the illustrated forms of the invention, the control means is energized to operate a power drive means in a reverse mode to retract the positioner to a home position. Upon coming to the home position, the control means is activated to start a forward mode of the power drive means to move the positioner toward the region to be occupied by the incoming workpiece and stop the power drive means when the positioner is positioned in accordance with the stored information. Desireably, the electrical control circuit is provided with a workpiece width comparison circuit to defeat respositioning of the reciprocator if the width of a new incoming workpiece is the same as the workpiece previously gaged.
In accordance with another feature of the present invention, the spray housing is provided with an automatic exit door arrangement. An actuator means is mechanically linked to the exit door arrangement and operationally connected to multiple delay timer means. The delay timer means can be activated at appropriate times in the part gaging and reciprocator positioning cycles and arranged to have a first time-out, when the conveyor means has transported the workpiece to the exit door arrangement, and a second time-out, when the workpiece has been transported through and beyond the exit door arrangement.
In the illustrated form of the invention, the exit door arrangement comprises two, opposed outwardly opening doors. Each of the opposed doors is of the "Dutch" door type and an actuator is mechanically linked to the upper portion of each door. If a small workpiece is about to exit, only the upper portions of the doors are opened by the actuator means. A sensing device, positioned adjacent the entrance of the spray housing, is activated by a workpiece that is higher than the upper portions of the exit doors. This will actuate a latch means to lock the bottom portions of the exit doors to the upper portions. Operation of the actuator means will now open both portions of the exit doors.